1. Field of the Invention
This invention generally relates to the field of a radio frequency identification (RFID) device. More particularly, the present invention relates to an RFID device to identify tags with the same identification code.
2. Description of the Prior Art
The use of RFID tags or cards to identify a person or an object is well known. In general, such tags, when excited, produce a magnetic field, or in some cases an electric field, of a first frequency, which is modulated with an identifying code. The tag may be either an active tag, i.e., a tag, which has a self contained power supply or, as is more usually the case, may be a passive tag that requires external excitation when it is to be read or disposed within the detection volume of a reader, for example, a door way or portal. In general, for portal type devices, passive type devices are utilized wherein a transmitting antenna for transmitting an exciting frequency signal for the tag is positioned at the portal and generally adjacent an antenna for receiving the modulated magnetic field, or electromagnetic field, produced by the excited tag in order to identify the tag, and consequently the user or object attached thereto.
In addition, the RFID tags can include different identification codes to be used in distinguishing different objects. For example, using different identification codes in the tags for staffs and visitors makes users be identified by reading the identification codes from a reader while the users pass through the door way.
As mentioned above, the reader identifies either a single tag or tags with different identification codes passing through the detection range. However, the reader cannot simultaneously identify the quantity of tags with the same identification code in the detection range. For example, the goods in a warehouse have tags for identification, and different kinds of goods have tags with different identification codes. A storekeeper can only get the quantity of the categories by using the reader, but cannot get the quantity of each kind of goods.
Hence, there is a need for an improved RFID system that can identify the amount of tags with the same identification, as well as detect in time variance in the quantity of tags within the detection range.